The band-gap energy Eg of silicon has been reevaluated with high precision between 2 and 300 K by the following method: the derivative of the absorption coefficient, resulting from free-exciton absorption, has a well-defined singularity, which can be detected unambiguously by wavelength-modulation spectroscopy. The energy of this singularity yields the band gap. Our data deviated by more than 5 meV from the earlier results of MacFarlane et al. and Haynes et al. and fell between their Eg(T) curves. The approximation of Eg(T) = A + BT + CT2 gives A = 1.170 eV, B = 1.059×10−5 eV/K, and C = −6.05×10−7 eV/K2, for 0<T≤190 K, and A = 1.1785 eV, B = −9.025×10−5 eV/K, and C = −3.05×10−7 eV/K2, for 150≤T≤300 K, which fits our data within 0.2 meV. The major uncertainty of about 1 meV lies in the energies of exciton and TO phonon.

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The refractive index of AlAs at 300 °K has been measured in the 0.5- to 2.2-eV range of photon energy. The long-wavelength dielectric constant with lattice vibrations neglected ε∞ is determined to be 8.16 ± 0.02, and the resulting static dielectric constant ε0 is 10.06 ± 0.04.

Experimental data on the wavelength dependence of the refractive index in the wavelength range 0.3–1.0 μm is presented for thin films of BaTiO3 and SrTiO3. The films of thickness 1–4 μm were prepared by sputter deposition at substrate temperatures of 300 to 600 K, resulting in amorphous films at the lower temperatures and ’’microcrystalline’’ films at the higher. Both thin-film phases have a lower index at a given wavelength than the corresponding crystalline value (e.g., at λ=5000 Å, n=2.00, 2.07, and 2.51 for amorphous, microcrystalline, and crystalline BaTiO3, respectively). The dispersion of the refractive index in the thin films follows a single-oscillator model with a higher oscillator energy and smaller oscillator strength than in the crystalline phase.